Optical fibers have an inherently large transmission capacity. Within a spectral interval which is no larger than 100 nm and which is centered at 1.55 .mu.m, the attenuation of an optical fiber is generally less than 0.2 dB/km. This spectral region alone yields more than 13 THz of extremely low loss transmission bandwidth. Other usable spectral regions which have only slightly higher attenuation provide additional transmission capacity.
Although still far from tapping the full transmission potential of optical fibers, recent experiments have demonstrated that very high bit rate transmissions can be achieved in a multi-wavelength optical network. (See for example: Kobrinski et al., "Demonstration of High Capacity in the Lambdanet Architecture: A Multiwavelength Optical Network", Electronics Letters, July 30, 1987, pp. 824-826.) From this perspective, it is reasonable to project numerous wavelengths being used simultaneously in future optical fiber networks. Accordingly, an essential building block of an optical fiber network is a switch which can be used to interconnect a plurality of optical fibers, each of which fibers carries a plurality of wavelengths.
At present most network switching is implemented electronically. Electronic technology is well developed and performs adequately for the present generation of communications networks which are based mainly on metallic cables with a growing share of point-to-point optical fiber trunks. As transmission data rates continue to increase, electronic switching and multiplexing components may become bottlenecks that prevent full utilization of the large bandwidth capacity of optical fibers. The reason is that electronic processing is inherently much slower than the transmission rates of optical fibers.
Although many kinds of optical switch elements have been proposed and investigated--most notably the Ti:LiNbO.sub.3 optical wavelength switches and the fiber coupler type mechanical switches--none of these are suitable for future multi-wavelength optical networks and, in particular, none are designed to switch individual wavelengths from specific input fibers to specific output fibers of a switch.
Accordingly, it is an object of the present invention to provide an all-optical switch involving no electronic processing which interconnects a plurality of input fibers and a plurality of output fibers and which can switch specific wavelengths from specific input fibers to specific output fibers. It is a further object of the invention to form such a switch from a matrix of 2.times.2 switching elements.